Electric initiators for explosives, pyrotechnics and propellants



Jam 14, 1964 c. R. HAMILTON ETAL 3,117,519

ELECTRIC INITIAToRs FOR ExPLosIvEs, PYRoTEcHNIcs AND PRoPELLANTs Filed Jan. 31, 1962 CHARLES R. HAMILTON WARREN R. HOELZEN MAURICE H. BROWN JOHN F. C SLEY ENTORS mi ZM ATTORNEYS atent p 3,117,519 Patented Jan. 14, 1964 3,117,519 ELECTRIC INITIATORS FOR EXPLOS'IVES, PYROTECHNICS AND PROPELLAN'IS Charles R. Hamilton, Riverside, Warren R. Hoelzen, '0ntario, Maurice H. Brown, Riverside, and John F. Crossley, Arlington, Calif., assignors to the United States of America as represented by the Secretary of the Navy Filed Jan. 31, 1962, Ser. No. 170,289 3 Claims. (Cl. 102-28) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to electric initiators and more particularly to improved electric initiators for explosives, pyrotechnics and propellants which are not susceptible to premature ignition when exposed to ordinary electrical sources and stray electromagnetic radiation.

The purpose of the present invention is to provide an electrically initiated primer, detonator, squib, or ignitor which is insensitive to the application of electrical energy at voltages below a predetermined level. This will result in eliminating hazards due to unintentional application of or exposure to ordinary electrical sources. It will also eliminate unintentional or accidental dudding of the device by damage resulting from ordinary sources of electrical energy which may not ignite the charge contained in the device.

Several attempts have been made in the past to overcome the problem of premature ignition of electrical initiators. Bridge wires which were made sufficiently heavy and low in resistance that a large current could be carried through them without causing them to either burn out or ignite the charge in the device were ineffectual when the device was connected to a low impedance source capable of exceeding the safe current. The degree of safety afforded by this method is therefore very limited, since many common sources can supply the energy required to initiate the device. Attenuating materials have been used to retard the fiow of alternating currents or transient currents through the bridge of the device but are effective only in preventing initiation of the device by relatively high-frequency alternating current or electromagnetic radiation. No protection is afforded from ordinary electrical power sources, of either alternating or direct current. Disconnection of the electrical circuits leading to the device and shorting its leads together or to a common ground to prevent application of electrical energy until it was desired to do so was effective only when the device is contained in the mechanism which accomplishes this. It is therefore hazardous or susceptible to damage before installation or at any time the associated protective device is opened or disassembled. The degree of safety is established by the protective device and not inherent in the initiator itself. Materials have been used for the charge in the device which were relatively insensitive to the amount of heat generated by application of electrical energy up to a certain level of power, but would be ignited when the electrical energy was applied at a sufficiently high level of power. This method provides no protection against accidental dudding of the device by destruction of the bridge by application of electrical energy sufficient to burn it out or melt it but not explode it. Also, the application of a voltage across the initiating bridge may result in establishing an arc discharge across the gap after the bridge is burned out; the arc may then continue until the charge is ignited. In some cases, application of direct current or radio frequency electromagnetic power at a level below that which would burn out the bridge can slowly heat the charge until it is ignited. Protection of the devices by enclosures or by precautions in handling affords Very indeterminate safety. Accidental initiation may result from unexpected or unknown power sources, particularly electromagnetic radiation which can not be observed.

Accordingly, an object of the present invention is the provision of an improved electrically initiated primer, detonator, squib, or ignitor which overcomes the above mentioned disadvantages of known devices.

Another object of the invention is to provide an electrically initiated primer, detonator, squib or ignitor which is insensitive to the application of electrical energy at voltages below a predetermined level.

A further object of the invention is the provision of an improved electric initiator which is safe against accidental ignition by alternating current, direct current or radiated electrical energy.

Still another object is to provide an improved electric initiator with means for measuring the gap breakdown voltage and bridge resistance after the device is completely assembled.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by references to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side elevation, in section, of a preferred embodiment of the invention.

FIG. 2 is a section of the device taken on the lines 2 2 of FIG. l with a portion of the material removed.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown an insulating plug 10, a metallic bridge 11, gap 14, test lead conductor 16 and power input conductors 12 and 13. Three electric circuits are established; first, power conductor 12, voltage gap 14, conductor 15, bridge 11 and power conductor 13; second, power conductor 12, voltage gap 14, conductor 15 and test lead conductor 16; third, test lead conductor 16, bridge 11 and power conductor 13. Ignition charge 17 and augmenting charge 18 are provided for igniting the explosive, pyrotechnic, or propellant charge. The ignitor is housed in a cup or capsule 19.

Electrical conductors 12, 13 and 16 are held in a fixed position by being molded into a glass, ceramic, plastic or any other suitable dielectric material. Input conductor 12 and test lead conductor 16 are formed by shaping a length of conductor with two right-angle bends. A contact surface 21 is provided at the base of the U-shaped member for soldering or welding one end of bridge member 11 thereto. Bridge 11 may be made of wire or it may be made of deposited metal film.

Gap 14 is fabricated by inserting the flat ends 22, 23 of conductor 12, which have been machined to eliminate any points, corners or small radii that may be present on the discharge surfaces, into a ceramic sleeve 24 which contains a gap spacer 25. An airtight seal is provided by means of a fused glass sleeve 26 surrounding the joint. Different breakdown voltage levels may be established by varying the length of gap spacer 25 or by inserting gas into the gap prior to sealing.

A well or recess 27 in which test lead 16 is located is provided to prevent the accidental application of electrical energy. Once the device has been tested by applying a test Voltage to conductor 16, the recess may be lled with a suitable potting compound thus insuring complete safety.

When ignition is required, the initiator is connected by means of conductors 12 and 13 to an electrical power source capable of delivering an electrical pulse at a voltage sufficiently high to establish an arc across gap 14 and with sufiicient energy to cause ignition of charge 17 by heating or exploding bridge 11. For testing the breakdown voltage of gap 14 a test source would be connected to conductors 12 and 16; and for testing the resistance of bridge 11 the test source would be connected to terminals 16 and 13. I Y

Obviously many modifications and variations of the present invention me possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended `claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. An electric initiator for explosives comprising:

(a) a casing for housing said initiator and being open only at one end,

(b) explosive material and electrically controlled ignition means therefor carried within said casing,

(c) said ignition means having iirst and second terminals, Y

(d) a iirst electrical conductor having one end connected to the first terminal of said ignition means and the other end terminating as one electrode of a voltage barrier means,

(e) a second electrical conductor having one end extending beyond the open end of said casing and adapted to be connected to a voltage source and the other end terminating as the second electrode of said voltage barrier means,

(f) a third electrical conductor having one end connected to the first terminal of said ignition means and the other end terminating within said casing,

(g) a fourth electrical conductor having one end connected to the second terminal of said ignition means 4 Vsurfaces of the electrodes of said voltage barrier means are plane and are separated by a ring shaped dielectric material to prevent conduction of current from the peripheries of said electrodes,

3. The device of claim l wherein said electrical conductors are molded in a dielectric material With said second and fourth conductors extending therefrom and said third `conductor is exposed in a recess in said molded material.

References Cited in the file or" this patent UNITED STATES PATENTS 2,103,759 Stupakoif Dec. 28, 1937 3,002,458 Haas Oct. 3, 1961 3,040,660 Johnston June 26, 1962 3,043,223 Clark July l0, 1962 3,052,185 Apstein Sept. 4, 1962 FOREIGN PATENTS 10,837 reat Britain 1904 

1. AN ELECTRIC INITIATOR FOR EXPLOSIVES COMPRISING: (A) A CASING FOR HOUSING SAID INITIATOR AND BEING OPEN ONLY AT ONE END. (B) EXPLOSIVE MATERIAL AND ELECTRICALLY CONTROLLED IGNITION MEANS THEREFOR CARRIED WITHIN SAID CASING, (C) SAID IGNITION MEANS HAVING FIRST AND SECOND TERMINALS. (D) A FIRST ELECTRICAL CONDUCTOR HAVING ONE END CONNECTED TO THE FIRST TERMINAL OF SAID IGNITION MEANS AND THE OTHER END TERMINATING AS ONE ELECTRODE OF A VOLTAGE BARRIER MEANS, (E) A SECOND ELECTRICAL CONDUCTOR HAVING ONE END EXTENDING BEYOND THE OPEN END OF SAID CASING AND ADAPTED TO BE CONNECTED TO A VOLTAGE SOURCE AND THE OTHER END TERMINATING AS THE SECOND ELECTRODE OF SAID VOLTAGE BARRIER MEANS, (F) A THIRD ELECTRICAL CONDUCTOR HAVING ONE END CONNECTED TO THE FIRST TERMINAL OF SAID IGNITION MEANS AND THE OTHER END TERMINATING WITHIN SAID CASING, (G) A FOURTH ELECTRICAL CONDUCTOR HAVING ONE END CONNECTED TO THE SECOND TERMINAL OF SAID IGNITION MEANS AND THE OTHER END EXTENDING BEYOND THE OPEN END OF SAID CASING AND ADAPTED TO BE CONNECTED TO THE SAME VOLTAGE SOURCE AS SAID SECOND ELECTRICAL CONDUCTOR, (H) WHEREBY AN IGNITION CIRCUIT IS ESTABLISHED THROUGH SAID IGNITION MEANS AND SAID FIRST, SECOND AND FOURTH CONDUCTORS, A FIRST TESTING CIRCUIT IS ESTABLISHED THROUGH SAID VOLTAGE BARRIER MEANS AND SAID FIRST, SECOND AND THIRD CONDUCTOR AND A SECOND TESTING CIRCUIT IS ESTABLISHED THROUGH SAID IGNITION MEANS AND SAID THIRD AND FOURTH CONDUCTORS. 